1. Field of the Invention
This invention relates to a device for detecting the quantity of liquid within a liquid container, for example, the quantity of the developing liquid within a liquid developing device in a copying machine.
2. Description of the Prior Art
Usually in copying machines of the liquid development type, the toner in the developing liquid is consumed with the process of copying and the concentration thereof is decreased while, at the same time, the quantity of the carrier liquid is also decreased, thus decreasing the quantity of the developing liquid within the developing device. It is therefore important to provide good copy images not only that toner or concentrated liquid be sometimes supplied to thereby maintain a predetermined concentration but also that the decrease in quantity of the liquid be warned or carrier liquid be supplied to maintain the liquid at a predetermined quantity.
Detection of the quantity of liquid within the developer container has heretofore been done as by detecting the position of a float on the liquid surface, optically detecting the liquid surface directly, or measuring the electrical resistance of the liquid corresponding to the differential of the liquid quantity.
Detection using a float has encountered difficulties in installation of the float and also required another switch for detecting the position of the float, and in addition, suffered from detection errors caused by the vibration of the liquid surface.
The optical method of directly detecting the level of the liquid surface by the use of a light source and a photoelectric element provided within the container has experienced a problem that when the liquid level is lowered, toner or other dust particles are deposited and solidified on the photoelectric element exposed, thereby aggravating the detection accuracy, or a problem that detection errors are induced by vibration of the liquid surface.
The detection of the liquid quantity utilizing the electrical resistance of the liquid might electrically impart an adverse effect to the liquid and is not preferable for the detection of the quantity of developing liquid.
When the liquid level is lowered, it is also usually the case that the air is sucked by a pump which pumps up the developing liquid and as the result, the air is formed into bubbles and mixed with the developing liquid. If the developing operation is continued with such bubbles created and remaining in the liquid, the resultant copy images will remarkably suffer from irregular developement or other deterioration in quality of image.
Such inconveniences could not quickly be overcome by any of the conventional detection methods.
Further, there is a well-known method of detecting the concentration of developing liquid by detecting the degree of transparency of the liquid with the aid of the light passed therethrough. However, in order to detect the quantity and concentration of the developing liquid and in addition, to maintain the quantity and concentration of the liquid at predetermined levels, different detector means must be mounted in the developing device and this is quite cumbersome.